Friday, November 17, 2006

Leonid Meteor Shower This Saturday:
The annual Leonid meteor shower will arrive this Saturday and will peak at 11:45 EST. This will be most visible in Western Europe and the Eastern seaboard of North America. in Western Europe the peak will be expected at 4:45 GMT. At this time Leo will be high in the southeastern sky just before sunrise. People here in Winnipeg and other areas of central North America will be disappointed as the peak viewing hours will be in or around dawn when Leo rises on the horizon.
The Leonids put on a spectacular display in 1966, despite the pessimistic predictions of many astronomers. One fireball from the display was 30 times brighter than the planet Venus, and the "meteor shower" became so intense in many places that it was impossible to keep accurate counts. more than 30 per minute were recorded in Arizona.
The Leonids are the "remains" of comet Temple-Tuttle, and they occur each year in mid-November. It's expected that many of the meteors will be visible even from urban locations. has provided a detailed guide to this celestial event.
Meteors are mostly the remains of passing comets or asteroids. When they pass through the Earth's atmosphere they are heated to over 3,000 degrees Fahrenheit. They are not actually heated by "friction" but rather by "ram pressure". When they enter the atmosphere they compress the air in front of them. The air heats up and, in turn, heats the meteor following behind it. Most meteors are vaporized by this heat. Some of them break up producing a fireworks-like display called a "fireball" and an explosion which can often be heard up to 30 miles away. Meteors which reach the ground are called "meteorites". A "meteoroid" is an object in space that may become a meteor if it hits the atmosphere.
How a meteor behaves depends on both its composition and the "angle of incidence" . Meteors falling at an oblique angle experience more stress, ad iron composition meteors withstand this stress better than "stony" or "cometary" meteors. Even iron based meteors will usually break up at an height of 7 to 5 miles up. If a meteor actually hits the ground it generally blasts out a crater 12 to 20 times its size. Larger meteors create not just a normal crater but also a "rebound effect" that creates a central peak.
Historical accounts of meteorites include an event in Connecticut in 1807 when several meteorites touched ground and, of course, the 1908 event in Tunguska, Siberia where many hundreds of square miles of forest were flattened by an exploding impact. The largest meteorite found in the USA weighed in at 2,360 pounds, and it was found in Nebraska in 1948. Big Boom to say the least. Meteor Crater in Arizona is one of the most famous sites of a meteor impact. The crater is 600 feet deep and about a mile wide. Evidence that the end of the Cretaceous age coincided with a massive impact off the coast of the Yucatan Peninsula has become pretty well standard theory in the last few decades. Throw a big enough smoke bomb and see what happens.
The best time to watch a meteor shower is usually in the early hours before dawn when the "leading edge" of our planet's rotation tends to catch oncoming meteors left by comets. yet this fact has to be put in place with the light conditions of viewing. Hence the poor viewing conditions where I live, in the central part of North America. The weather report, by the way, predicts clear skies for the night of the 18th/19th,;so you can bet I'll be out there in early dawn. Many flares of activity may also be seen tonight and Sunday.
Keep watching the sky;

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